This invention relates to an alutriator, and more particularly relates to an elutriator for separating different grades of leaf or fibrous vegetable material.
Known apparatus for the separation of different grades of leaf vegetable material generally includes a rapidly flowing upward air stream into which the material is fed.
The principle involved in such apparatus is that different grades of leaf vegetable material have different terminal velocities. Consequently those grades with lower terminal velocities should rise in the upward air stream to the top of the apparatus from where they can be removed; those grades with higher terminal velocities should fall to, or remain at the bottom of the apparatus.
In practice it is difficult to achieve an efficient separation, and it is often necessary to recycle part of the separated material several times, or to pass it through additional separating apparatus.
In prior devices the upward air flow rate has been much higher than the lowest terminal velocity of the grades of leaf material in order to separate acceptable amounts of low terminal velocity material.
However, the provision of such high air velocities causes turbulence which can disadvantageously affect the efficiency of the separation.
One way in which this problem has been partially overcome is by winnowing (i.e. throwing) the leaf vegetable material upwardly into the apparatus at high velocity. This improves the efficiency of the separation, but leads to degradation by breakage and bruising and increased running costs; it is also necessary to use air locks in the apparatus, and these increase the possibility of blockages and build-ups in the material flow.